Abstract

Finite Element analysis has been slow to be applied to the general design of submarine pressure vessels, in part because of the reliability and efficiency of traditional semi-empirical methods, and partly, as an unstable buckling problem, it is quite difficult to solve. This paper will describe the development of a standardised approach to predicting the collapse behaviour of submarine pressure hulls. These can be deceptively simple structures, usually axisymmetric ring-stiffened cylinders, cones, hemispheres and occasionally other curved profiles, and the only significant design load is uniform hydrostatic pressure. However, the collapse process is difficult to model accurately as it involves geometric non-linearity, elasto-plastic material behaviour and loss of stability. The strength of a hull is sensitive to a range of fabrication effects such as; shape imperfections, dimensional variations and residual stresses due to cold bending of plating and welding. These effects have been assessed during the development of the standardised approach and the accuracy of the process has been quantified against experimental data and conventional analytical, and semi-empirical, solutions. A plugin that captures this process has been written for Abaqus, (although the process could be implemented in any general-purpose FE code). It allows quick generation of consistent, repeatable models, while providing the user with a degree of flexibility in the model details and analysis approach. A range of allowable shape imperfections in the form of critical buckling modes and other fabrication effects can be combined to create an idealised as-built or design shape. The algorithms in the plugin have also been adapted for use with process automation and optimisation software to carry out formal optimisation and ‘design of experiments’ studies, allowing the process to be used effectively in pressure hull design cycles. Capturing this process in a design standard will encourage the use of FE analysis in the design process, which will in turn allow designers to exploit the full capability of FE to expand their design horizons.